Key Factors for APF in VRF Systems

In this study, simulation and experimental testing were carried out in a 28 kW variable refrigerant flow system to evaluate the contributions to annual performance factor (APF) from key factors, including heat exchanger area, compressor efficiency, refrigerant charge, system pressure loss, and oil return system. The APF values obtained experimentally and numerically are 4.59 and 4.61, respectively. Meanwhile, the maximum deviation between simulation and experiment is 5.1% at a single test condition, and the deviation of the APF is 0.5%. The results show that for the experimental system, the improvement in a single factor has a limited effect on the APF. For example, if the compressor efficiency increases by 3%, the APF increases by 2.8%. The optimization of the oil return system leads to an approximately 5% increase in the APF. A 10% increase in KA of the heat exchanger results in a 1% improvement of the APF. Therefore, many factors must be considered simultaneously to improve the APF.